Heating apparatus switch



Aug' 5, 1947. E. K. CLARK ZAZ HEATING APPARATUS SWITCH Filed Sept. 22,1942 5 Sheets-Sheen 2 55 sa 5a 15g.

INVENTOR EARL, V. CLARK ATTORNEY Allg. 5, 1947. E, K, CLARK 2,425,030

HEATING APPARATUS SWITCH Filed Sept. 22, 1942 3 Sheets-Sheet 3 L Ll CL"N 7 f LL 2.

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21 62. 22 c/ c! /y /45 /64'5 MNM/4L AAW/4L wlTNEss-s: n v C7 7 INVENTORG F Emu. Ka (imm BY o I l* y A oRNEY Patented Aug. 5, 1947 2,425,030HEATING APPARATUS SWITCH Earl K. Clark, Mansfield, Ohio, assigner toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Appiieeaep september 22, 1942, serial No. 459,253

7 Claims. l

This invention relates to heating apparatus and particularly to acontrol device therefor which is especially adapted to control thewattage input to the heating apparatus, and it has for an object toprovide an improved device of the character set forth.

It is also an object of the invention to provide a control including athermally-operated cycling switch wherein the wattage input to theheating apparatus is not materially affected by variations in ambienttemperatures at the control and, therefore, it is not necessary tocompensate for ambient temperature changes.

It is another object of the invention to provide a control including athermallyoperated cycling switch in which the switching cycles are ofsubstantially uniform duration irrespective of normal changes in ambienttemperatures eilecting the control switch, and regardless of theselected wattage input to the heating apparatus to be con trolled.

It is a still further object of the invention to provide athermally-operated cycling switch in which the circuit-making andcircuit-breaking switching operations are such that the time intervalduring which the circuit is closed may be adjusted to an extremely shortinterval to provide a minimum wattage input to the circuit controlled bythe switch.

These and other objects are eiected by my invention as will be apparentfrom the following description and claims taken in connection with theaccompanying drawings, forming a part of this application, in which:

Fig. l is a perspective view of an electric cooking range in which thepresent invention is incorporated;

Fig. 2 is an .elevational view of the present control with the coverthereof removed and parts shown in section;

Fig. 3 is a fragmentary elevational view corresponding to a portion ofFig. 2 and showing the movable parts in a position different from thatin Fig. 2; I

Fig. 4 is a sectional view taken substantially on the line IV--IV ofFig, 2;

Fig. 5 is a. diagrammatic view of the control shown in the previousfigures and including a wiring diagram to illustrate one application ofthe invention;

Figs. 6 and 7 are diagrammatic views similar to Fig. 5 but omitting thewiring diagram and showing the position of the switch contacts atdifferent points in a cycle of operation of the control; and

(Cl. 20o-122) Figs. 8 and 9 are time-temperature graphs illustrating thecycle of the thermal motor employed in the present control and showingthe ef fect of changes in ambient temperature at the motor.

The control, generally indicated I0, comprises two sets of contacts IIelectrically connected in series as shown particularly in Fig. 5 and athermal motor, generally indicated as I2 in Figure 2, whichintermittently opens and closes these contacts. When both sets ofcontacts are closed, they complete a circuit for an electricalresistance element such as I3 in Fig. 5, which may be a surface heatingelement or an oven heating element of the range shown in Fig. 1. Thecontrol isV adjustable so that the ratio between the length of time bothsets of contacts are closed to the length of time one or the other ofthem is open to interrupt the circuit may be varied to provide apreselected Wattage input to the resistance element I3. y g

Thel control is arranged in a compact housing I4 preferably made ofinsulating material and provided with a cover (not shown). The housingmay be conveniently mounted at the rear of the backsplasher of the rangeshown in Fig. 1, as illustrated by dotted lines, with its adjusting knobI5 accessible at the front. I'he housing carries two supply lineterminals I8 having fixed contacts I 'I which are engageable by movablecontacts I8 carried by long springs I9. These springs are fixed toterminal brackets 2| and 22 at the lower end of the housing- The movablecontacts I8 are moved into and out of engagement with their respectivefixed contacts II by means oi' a cam 23. This cam is provided withnotches 24 laterally offset relative to each other and which are adaptedto receive integral lug portions 25 of the springs I9 when the controlis set at its off position. The off position of the control I0 is shownin Fig. 2 where it will be noted that the lugs 25 are received in thenotches 24, the natural bias of the springs holding contacts I 'I and I8open.

Cam 23 is xed on a shaft 26, journaled in the rear wall of the. housing,as shown in Fig. 4. By rotating the knob I5 from its "ofP position, thelugs 25 ride on the cylindrical surface of the cam 23 to maintainthe-movable contacts I8 in engagement with fixed contacts II as shown inFig. 3.

It will be understood that supply conductors, such as L1 and La of aconventional Edison threewire system, are connected to the terminals I6as shown in Fig. 5 and that the contacts Il and I8 comprise adouble-pole line switch to control 3 the supply of electricity to thethermal motor I2 and to the circuit controlled by the device of thepresent invention.

The thermal motor I2 is mounted in the lower portion of the housing andcomprises a bimetal member 21 xed to a bracket 28 which may beadjustably secured to the bottom wall of the housing to permitadjustment of the bimetal with respect to the cycling contacts II. Theupper free end of this bimetal has riveted thereto a U-shaped spring 23which is received in an opening 3l provided in a horizontal bar 32 andprevents lost motion between the bimetal and bar.

The bimetal 21 is intermittently heated by means of a resistance 33which is shown schematically as wrapped about the bimetal, although itis to be understood that the bimetal heating means may be associatedwith the bimetal in any suitable manner. When the resistance isenergized to heat the bimetal, the |bimetal bows to the left, as viewedin Fig. 2, and upon deenergization of the heater, the bimetal cools andmoves to the right.

The right end of the bar 32, which, it will be understood is moved bythe bimetal, is provided with a depending bracket 34 which carries astop and switch-operating stud 35. This stud passes through and isjournaled in an opening 33 provided in a plate 31 secured to the housingI4 by means of ears 38 integrally formed thereon and fastened to bosses39 provided on the side wall of the housing.

By reference to Figs. 2 and 3, it will be noted that the travel of thebar 32 to the right is limited by engagement of the bracket 34 with theplate 31, as shown in Fig. 2, and travel to the left by engagement ofshoulder 4I of the stud 35 with the plate 31, as shown in Fig. 3.

The stud 35 also operates a switch which controls the energization ofthe bimetal heating element 33. This switch comprises an adjustablecontact screw 42 threaded into the side wall of the housing and acooperating contact 43 carried by a snap-acting spring member 44,preferably of the so-called Valverde type. The snap-acting member 44comprises three legs connected together at their ends, the outer legs 45being made shorter than the central leg 43, as by crimping. The centerleg 45 is ilxed to plate 31 by means of a stud 41.

The operation of the switch, comprising contacts 42 and 43 for thebimetal heater 33 is briefly as follows: In Fig. 2 the parts are shownin the position they assume when the bimetal 21 has cooled sufcientlyfor the bar 32 to reach its extreme right position at which time thestud 35 has caused the snap-acting spring 44 to snap over to theposition shown in this gure and close the contacts 42 and 43. With thesecontacts closed. a circuit is established from neutral conductor N ofthe supply source (Fig. 5), through the closed contacts 42--43,conductor 48, the heating element 33, conductor 49, terminal 22, rightspring member I9 and closed contacts I8 and I1 of the line switch to L1of the supply line. With this circuit complete, heating element 33 heatsthe bimetal causing it to bow to the left, as viewed, in Fig. 2, to movethe bar 32 and the stud 35 carried thereby to the .position shown inFig. 3 by which time nut 5I carried by the stud causes the snap-actingspring 44 to snap over to the position shown in Fig. 3 and open contacts42 and 43 and thereby deenergize the bimetal heating element.

When the snap-acting spring 44 snaps over to open the contacts 42 and43, the lower free end of this spring engages an adjustable stop 52carried by the plate 31, as shown in Fig. 3. It will be appreciated thatthe contact screw 42 and stop 52 may be adjusted relative to each otherand to the lower free end of the snap-acting spring 44 so that thesnap-acting spring may be made to operate between the limits determinedby the length of travel of the switch-actuating stud 35.

With the bimetal heating element 33 deenergized, the bimetal 21 beginsto cool and moves the bar 32 to the right until it reaches the positionshown in Fig. 2 at which time the cycle described above will berepeated.

The bar is continuously reciprocated as long as the line switch contactsI1-I8 are closed and as will appear later intermittently opens andcloses the switch contacts I I during the middle of its travel whileeffecting switching of contacts 42 and 43 at each end of its travel. Inother words, the cycling switches II are actuated in spacedtime relationto the actuation ot the switch 42 43. Each set of cycling contacts IIinclude an adjustable contact 53 and a movable contact 54 biased towardits respective adjustable contact 53. The contacts 53 are simultaneouslyadjustable relative to their respective movable contacts 54 to vary thelength of time both sets of contacts 53--54 are closed during each halfcycle of the thermal motor I2 to increase or decrease the averagewattage input to the resistance I3 controlled by these contacts. Themanner of operating these contacts and adjusting them to vary thewattage input to the controlled circuit is described hereinafter.

The adjustable contacts 53 are carried by contact bars 55 which arefixed to the free ends of a U-shaped spring member 55 iixed to the upperend wall of the housing I4. This spring member serves to electricallyconnect, the contact bars 55 and their contacts 53 and is so arrangedthat it biases the bars toward each other, to maintain adjustable stopsor screws 51 carried thereby, in engagement with cams 58 and 53,respectively.

The cams 58 and 53, are fixed to the shaft 26, and are identical andarranged so that they simultaneously swing the contact bars 55 away fromor toward each other as the shaft is turned by knob I5.

The movable contacts 54 are mounted on arms 5I which are, in turn,hingedly mounted on terminal brackets 52 and 22, respectively, by meansof spring strips 53. These spring strips are so arranged that they tendto bias the contacts 54 into engagement with their respective adjustablecontacts 53. The arms 6I extend through openings 64 and 55 provided inthe reciprocating horizontal bar 32.

From the above description, it will be seen that with the line switchcontacts I1 and I8 closed, the horizontal bar 32 continuouslyreciprocates and that by proper association 0f the openings 64 and 65through which the arms 8l extend, these arms and their contacts 54 arealternately moved in a direction away from and, due to the bias of theirhinge springs 63, toward their respective movable contacts 53.

Operation It will be seen that in the condition shown in Fig. 2, withthe control knob I5 set at "off, the line switch contacts I1 and I8 areheld open and that the right-hand pair of contacts 53 and 54 of thecycling switch are also open. However, on turning the adjusting shaftfrom its o position to an active position, the condition represented inFig. will result, wherein the line switch contacts I1 and IB are nowclosed causing energization of the bimetal heater 33 as alreadyexplained. It will be understood that turning of knob I5 from its offposition causes cams 58 and 53 to swing the movable contacts 53outwardly away from each other and toward their respective movablecontacts 54. With the re sistance 33 energized, the bimetal 21 begins tobow to the left and moves the horizontal bar 32 to the left permittingthe right-hand contact arm 6I and its contact 54 to approach theright-hand adjustable contact 53 until the switches are in the positionshown in Fig. 6. At this time both sets of the cycling contacts areclosed since the bar 32 has not yet begun to move the left-hand Contactarm 5I. An energizing circuit for the resistance I3 is now complete.This circuit may be traced in Figs. 2 or 5 from one side L1 of thesupply line, closed contacts Il and I8 of the line switch, through rightspring I9, terminal bracket 22, right contact arm 6I, closed cyclingcontacts 53 and 54 and their connecting spring 56, left contact arm 6I,conductor 51 to one side of the Y heating element I3 and from the otherside thereor through the left spring I9 and closed contacts Il and I8 ofthe line switch to the other side L2 of the supply line.

However, the bimetal continues to be heated until the bar reachessubstantially its extreme left position, as shown in Fig. 3, but beforethis occurs, the left pair of cycling contacts 53 and 54 will haveopened, as shown in Fig. '7, to interrupt the circuit just described..Thus, the energizing circuit for the heating element I3 is completedduring a portion only of \the time it takes the bar 32 to travel fromright\to left through the heating-up period of the bimetal 2l. Similarlyduring the cooling-down period of the bimetal, the same sequence ofoperations described above in connection with the cycling switchcontacts 53 and 54 is repeated except that the left pair of cyclingcontacts53 and 54 close to complete the circuit and the rigift pair ofcontacts open to interrupt the circuit. It will be understood thatv cams58 and 59 adjustably position the contacts 53 to fix the ratio betweenthe period o! time the contacts 53 and 54 are simultaneously closed tothe period they are open for each cycle of the bar 32. Thus, if contacts53 and 54 are both closed for one-half the time cycle of the bar 32,one-half wattage input is Provided for the heating element I3.

For each complete cycle of the bimetal motor, that is, a completereciprocation of the bar 32, the energizing circuit for the heatingelement is established twice and by selecting a bimetal 21 and heaterwhich provides a two minute cycle, the heating element I3 is energizedtwice every two minutes. Thus, while this .is an on and off control, thecycle is suiliciently short so that the eiect is substantially the sameas varying continuous wattage input. A further advantage arising fromthe present arrangement of the cycling contacts is that for each halfcycle of the bimetal motor, one pair of cycling contacts completes theenergizing circuit and the other pair o! cycling contacts interrupts thecircuit so that the life of these contacts is doubled as compared tocycling contacts wherein the same set of contacts interrupts andcompletes the circuit.

The cams 53 and 59, which position the contact arms 55 and theircontacts 53 with respect to the associated movable contacts 54, arepreferably shaped so that, within the low wattage range of adjustmentwhich provides relatively short on periods for the heating element i3,relatively great movement of the knob is require-d to effect a smallchange in the wattage input and the adjustment in the higher wattageinput range is relatively coarse so that a small movement of theadjusting shaft effects a substantial change in the wattage input to theheating ele ment I3. It is understood that the knob i5 will be providedwith a suitable scale. v

By providing the on period for the resistance element I3 lat the centerel" the heating and cooling periods of the bimetal motor, it is possibleto obtain a minimum time on interval. to provide an extremely lowwattage input to the resistance element. For example, if the on intervalwere at either end of the thermal cycle of the Minetti motor, the threefollowing factors would ce instrumental in adding to the minimum time oninterval obtained at the minimum switch setting. These factors are:

(l) .Annulment of the bimetal deflection as a result of engagement ofthe bimetal with the cycling switch contact. `That is, movement oi thebimetal is arrested until it develops enough crce to overcome the springbias exerted by the switch contact arm.

(2) Annulment of the bimetal deflection as a result of operating thebimetal motor switch,

f which must be snap-acting.

(3) The time interval required for the himetal to change its directionof deection at the end of its thermal cycle due to thermal storage andlag of the bimetal heating element.

The present control eliminates factor 2 in that the cycling contacts areactuated at a time other than when the bimetal is actuating snapactingbimetal switch and it also eliminates iacm tor 3 since the bimetalactuates the cycling con tacts in the middle of its travel, while thethermal storage and lag of the bimetal heating element is eiective onlyat` the ends of the heating and cooling periods of the bimetal.

The graphs of Figs. 8 and 9 illustrate the fact that normal changes inambient temperature at the bimetal 21 have little effect on the cyclingperiod of the bimetal and the wattage input to been plotted against timefor a complete cycle of the thermal motor. 'The lower horizontal line Arepresents the temperature at which the bimetal heater switch 42--43closes and the upper horl- Zontal line B the temperature at which thiskswitch opens. Thus, beginning at the point C in the graph of Figli, thehimetal temperature rises along the curve D initil the upper temperaturelimit B is reached, asA indicated 'oy point at which time the switch42-43 opens to deenerM gize the bimetal heater. The himetal then coolsalong the curve F until the lower temperature limit A is reached atpoint G when the switch 42-43 again closes to begin. a new cycle. Thegraph of Fig. 8 gives an'approi-.imate timetemperature indication withan assumed ambient temperature of'ilO F. at the bimetal.

In Fig. 9 the same cycle has been plotted out with an assumed ambienttemperature of F. It will be noted that with the higher ambient temperature the heating period of the loimctal is shorter but the coolingperiod is longer than with 7 the lower ambient temperature, with theresult that the length cf the cycles is substantially the same for thedifferent ambient temperatures.

As previously explained, both sets of cycling contacts 53--54 are closedduring the middle of the travel of the bimetal on its heating andcooling periods, and the length of time these contacts are closed foreach cycle of the bimetal determines the average wattage input to theheating element I3.

Ln Figs. 8 and 9, the horizontal lines H and I respectively indicate thelower and upper bimetal temperature limits between which the bimetalcauses both sets of cycling contacts 53--54 to be closed for aparticular setting of the knob I5. It will be understood that differentsettings of the knob change these limits to provide different averagewattage inputs to the heating element I3, The points J, K, L, and Mwhere the lines H and I intersect the curves D and F, represent thepoints at which the bimetal effects switching of the contacts |53 and54. The horizontal distance between related points J, K, and L, Mdetermines the time the contacts 53-54 are closed for a complete cycleof the bimetal. The ratio of the time between J and K, represented by X,to the total heating-up period, represented by Y gives the per cent ofmaximum wattage input to the heating element for the heating-up periodof the bimetal. Similarly the ratio between the time X', the horizontaldistance between L and M, to the coollng-down period Y' gives the percent of maximum wattage input to the heating element for thecooling-down period of the bimetal. These ratios are substantiallyidentical.

It will be noted from Figs. 8 and 9 that, since the portion of each ofthe heating and cooling curves during which the contacts are closed islocated in the center of the curve, its slope will be substantially thesame as the general slope of the complete heating or cooling curve. Thisis true even though the slope of the curve changes for different ambienttemperatures. Accordingly, the percentage of time that the contacts areclosed during each heating or cooling period remains substantially thesame upon change in ambient temperature.

The present control is particularly adapted for use in a control systemlike that disclosed in Pat ent No, 2,399,423 of Edward Bletz, assignedto the assignee of the present invention. The Bletz control systemincludes a thermostatic switch which is responsive to the temperature ofa body to be heated. such as a cooking vessel or the like placed on asurface heating element of a range, and arranged so that maximum wattageinput is initially supplied to the heating element to rapidly heat thebody. When the body reaches a predetermined temperature, it causes thethermostatic switch to open, and control of the energization of theheating element is shifted to a wattage selector which may, for example,be the present control.

As shown particularly in Figs. 2 and 5, such a thermostatic switch,generally indicated T, may be connected in parallel to the cyclingcontacts 63-54 so that when the thermostatic switch is closed thesecontacts are shunted and continuous energization of the resistance I3 isprovided but when the temperature of the heated body and thethermostatic switch reaches a preselected value, the thermostatic switchopens and energization of the resistance I3 is then controlled by thecycling contacts 53-54.

While I have shown my invention in but one form, it will be obvious tothose skilled in the art 8 that it is not so limited, but is susceptibleof various changes and modifications without departing from the spiritthereof, and I desire. therefore, that only such limitations shall beplaced thereupon as are specifically set forth in the appended claims.

What I claim is:

1. A control comprising a pair of series connected switches eachincluding an adjustable contact and a movable contact, means foradjusting said adjustable contacts relative to their respective movablecontacts, and reciprocating means for moving said movable contacts toclose .both pairs of contacts during the intermediate portion of itstravel. to open one pair of ccntacts at one end of its travel and toopen the other pair of contacts at the other end of its travel. saidlast-mentioned means comprising a thermal motor and a heater therefor,and switch means actuated by said motor and independent of saidfirst-mentioned switches for controlling said heater. 4

2. A control device comprising a casing, a rotatable shaft in saidcasing and having handle means thereon for manually rotating said shaft.cam means carried by said shaft within said casing, adjustable contactarms disposed within said casing and biased into engagement with saidcam means, a pair of movable contact arms mounted within said casing andhaving contact portions adapted to engage contact portions on saidadjustable contact arms, means for moving said pair of movable contactarms in a regularly repeated cycle, said last-mentioned means beingoperable during each cycle to move one movable contact arm out of andinto engagement with its associated contact portion and then to move theother movable contact arm out of and into engagement with its associatedcontact portion. said cam means being effective on adjustment of saidshaft to position said contact portions of said adjustable contact armsto engage said movable contact portions for varying periods.

3. A control device for an electrically-energized element comprising rstswitch means'for controlling the supply of electrical energy to saidelement, reciprocating means movable in a nxed path and actuating saidswitch means to cause alternate energization and deenergization of saidelement, the energization of said element taking place in a centralportion of said path and deenergization of said element taking place ineach end portion of said path, thermal-motor means including atemperature-responsive means and a heater therefor for moving saidrecpirocating means, and second switch means for controllingenergization o! said heater and actuated by said reciprocating means atthe ends of said path.

4. A control device for an electrically-energized element comprisingfirst switch means for controlling the supply of electrical energy tosaid element, reciprocating means for actuating said switch means tocause alternate energization and deenergization of said element. saidreciprocating means actuating said switch means to close the circuittherethrough in the central portion of its travel and to open thecircuit therethrough in each end portion of its travel, andthermal-motor means including a temperature-responsive means and aheater therefor for driving said reciprocating means, and second switchmeans for controlling the energization of said heater and actuated bysaid reciprocating means at the ends of its travel.

5. A control device for an electrically-enerbring the movable contact ofsaid iirst switch into engagement with its adjustable contact andsubsequently move the movable contact of the second switch out ofengagement with its adjustable contact when moving in one direction andto bring the movable contact of said second switch into engagement withits adjustable contact and subsequently move the movable contact of saidfirst switch out of engagement with its adjustable contact when movingin the opposite direction, thermal-motor means for moving saidreciprocating means in said path, said thermalmotor means including aswitch actuated by said reciprocating means in spaced-time relation tothe actuation of said first-mentioned switches.

6. An electrical control device comprising nrst switch means for openingand closing a circuit therethrough and including first and Secondactuating members each of which is adapted when actuated to open saidcircuit, reciprocating thermal-motor means for' alternately actuatingsaid members, said thermal-motor means including reciprocatingtemperature-responsive means and a heater therefor, and second switchmeans for initiating energization of said heater when said thermal-motormeans reaches one end of its travel and for initiating deenergization ofsaid heater when said thermal-motor means reaches the other end of itstravel, said thermal-motor means being operable throughout one endportion of its travel to actuate one of said members to open the iirstswitch means and throughout the other end portion of its travel toactuate the other member to open said rst switch means, said nrst switchmeans being closed only during a central portion of the travel of saidthermal-motor means.

7. A control comprising a pair of switches connected in series with eachother, each o! said switches including an adjustable contact and amovable contact, means including a common manually-actuated member foradjusting said adjustable contacts with. respect to said movablecontacts, said last-mentioned means being operable to adjust 4both ofsaid adjustable contacts toward their associated movable contacts uponmovement of said member in one direction and away from the same uponmovement in the opposite direction, motor means for moving said movablecontacts into and out of engagement with said adjustable contacts in aregularly repeated cycle, said last-mentioned means being operableduring each cycle to move one movable contact out of and into engagementwith its associated adjustable contact while the other contacts are inengagement and then to move the other movable contact out of and intoengagement with its associated adjustable contact while the firstcontacts remain in engagement, whereby the circuit through theseries-connected switches is opened once by each switch duringeach cycleof operation and whereby\both periodscf circuit opening in each cycleare adjusted by said common manually-actuated member,

EARL K CLARK.

file of this patent:

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